System for selecting the operating frequency of a communication device in a wireless network

ABSTRACT

A system for automatically selecting communication frequencies for wireless communication devices (e.g., base unit, access point, and controller) being added to an existing wireless network. The operating frequencies, evaluated signal strength, and loads are used in determining the most suitable operating frequency. This automatic selection process eliminates the problems inherent in manual frequency selection.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/802,985, filed on Mar. 17, 2004, which is a continuation of U.S.application Ser. No. 09/477,842 filed on Jan. 5, 2000, now U.S. Pat. No.6,732,163.

FIELD OF INVENTION

The present invention relates generally to a wireless communicationsystem, and more particularly to a system for automatically selectingcommunication frequencies for wireless communication devices.

BACKGROUND OF THE INVENTION

The use of wireless networks has become prevalent throughout the modernworkplace. For example, retail stores and warehouses may use a wirelesslocal area network (LAN) to track inventory and replenish stock andoffice environments may use a wireless LAN to share computerperipherals. A wireless LAN offers several advantages over regular LANs.For example, users are not confined to locations previously wired fornetwork access, wireless work stations are relatively easy to link withan existing LAN without the expense of additional cabling or technicalsupport; and wireless LANs provide excellent alternatives for mobile ortemporary working environments.

In general there are two types of wireless LANs, independent andinfrastructure wireless LANs. The independent, or peer-to-peer, wirelessLAN is the simplest configuration and connects a set of personalcomputers with wireless adapters. Any time two or more wireless adaptersare within range of each other, they can set up an independent network.In infrastructure wireless LANs, multiple base stations link thewireless LAN to the wired network and allow users to efficiently sharenetwork resources. The base stations not only provide communication withthe wired network, but also mediate wireless network traffic in theimmediate neighborhood. Both of these network types are discussedextensively in the IEEE 802.11 standard for wireless LANs.

In the majority of applications, wireless LANs are of the infrastructuretype. That is, the wireless LAN typically includes a number of fixedbase stations, also known as access points, interconnected by a cablemedium to form a hardwired network. The hardwired network is oftenreferred to as a system backbone and may include many distinct types ofnodes, such as, host computers, mass storage media, and communicationsports. Also included in the typical wireless LAN are intermediate basestations which are not directly connected to the hardwired network.

These intermediate base stations, often referred to as wireless basestations, increase the area within which base stations connected to thehardwired network can communicate with mobile terminals. Associated witheach base station is a geographical cell. A cell is a geographic area inwhich a base station has sufficient signal strength to transmit data toand receive data from a mobile terminal with an acceptable error rate.Unless otherwise indicated, the term base station, will hereinafterrefer to both base stations hardwired to the network and wireless basestations. Typically, the base station connects to the wired network froma fixed location using standard Ethernet cable, although in some casethe base station may function as a repeater and have no direct link tothe cable medium. Minimally, the base station receives, buffers, andtransmits data between the wireless local area network (WLAN) and thewired network infrastructure. A single base station can support a smallgroup of users and can function within a predetermined range.

In general, end users access the wireless LAN through wireless LANadapters, which are implemented as PC cards in notebook computers, ISAor PCI cards in desktop computers, or fully integrated devices withinhand-held computers. Wireless LAN adapters provide an interface betweenthe client network operating system and the airwaves. The nature of thewireless connection is transparent to the network operating system.

In general operation, when a mobile terminal is powered up, it“associates” with a base station through which the mobile terminal canmaintain wireless communication with the network. In order to associate,the mobile terminal must be within the cell range of the base stationand the base station must likewise be situated within the effectiverange of the mobile terminal. Upon association, the mobile unit iseffectively linked to the entire LAN via the base station. As thelocation of the mobile terminal changes, the base station with which themobile terminal was originally associated may fall outside the range ofthe mobile terminal. Therefore, the mobile terminal may “de-associate”with the base station it was originally associated to and associate withanother base station which is within its communication range.Accordingly, wireless LAN topologies must allow the cells for a givenbase station to overlap geographically with cells from other basestations to allow seamless transition from one base station to another.

Most wireless LANs, as described above, use spread spectrum technology.Spread spectrum technology is a wideband radio frequency techniquedeveloped by the military for use in reliable, secure, mission-criticalcommunication systems. A spread spectrum communication system is one inwhich the transmitted frequency spectrum or bandwidth is much wider thanabsolutely necessary. Spread spectrum is designed to trade off bandwidthefficiency for reliability, integrity, and security. That is, morebandwidth is consumed than in the case of narrowband transmission, butthe tradeoff produces a signal that is, in effect, louder and thuseasier to detect, provided that the receiver knows the parameters of thespread spectrum signal being broadcast. If a receiver is not tuned tothe right frequency, a spread spectrum signal looks like backgroundnoise.

In practice, there are two types of spread spectrum architectures:frequency hopping (FH) and direct sequence (DS). Both architectures aredefined for operation in the 2.4 GHz industrial, scientific, and medical(ISM) frequency band. Each occupies 83 MHz of bandwidth ranging from2.400 GHz to 2.483 GHz. Wideband frequency modulation is an example ofan analog spread spectrum communication system.

In frequency hopping spread spectrum systems the modulation processcontains the following two steps: 1) the original message modulates thecarrier, thus generating a narrow band signal; 2) the frequency of thecarrier is periodically modified (hopped) following a specific spreadingcode. In frequency hopping spread spectrum systems, the spreading codeis a list of frequencies to be used for the carrier signal. The amountof time spent on each hop is known as dwell time. Redundancy is achievedin FHSS systems by the possibility to execute re-transmissions onfrequencies (hops) not affected by noise.

Direct sequence is a form of digital spread spectrum. With regard todirect sequence spread spectrum (“DSSS”), the transmission bandwidthrequired by the baseband modulation of a digital signal is expanded to awider bandwidth by using a much faster switching rate than used torepresent the original bit period. In operation, prior to transmission,each original data bit to be transmitted is converted or coded to asequence of a “sub bits” often referred to as “chips” (having logicvalues of zero or one) in accordance with a conversion algorithm. Thecoding algorithm is usually termed a spreading function. Depending onthe spreading function, the original data bit may be converted to asequence of five, ten, or more chips. The rate of transmission of chipsby a transmitter is defined as the “chipping rate.”

As previously stated, a spread spectrum communication system transmitschips at a wider signal bandwidth (broadband signal) and a lower signalamplitude than the corresponding original data would have beentransmitted at baseband. At the receiver, a despreading function and ademodulator are employed to convert or decode the transmitted chip codesequence back to the original data on baseband. The receiver, of course,must receive the broadband signal at the transmitter chipping rate.

The coding scheme of a spread spectrum communication system utilizes apseudo-random binary sequence (“PRSB”). In a DSSS system, coding isachieved by converting each original data bit (zero or one) to apredetermined repetitive pseudo noise (“PN”) code.

A PN code length refers to a length of the coded sequence (the number ofchips) for each original data bit. As noted above, the PN code lengtheffects the processing gain. A longer PN code yields a higher processinggain which results in an increased communication range. The PN codechipping rate refers to the rate at which the chips are transmitted by atransmitter system. A receiver system must receive, demodulate anddespread the PN coded chip sequence at the chipping rate utilized by thetransmitter system. At a higher chipping, the receiver system isallotted a smaller amount of time to receive, demodulate and despreadthe chip sequence. As the chipping rate increases so to will the errorrate. Thus, a higher chipping rate effectively reduces communicationrange. Conversely, decreasing the chipping rate increases communicationrange. The spreading of a digital data signal by the PN code effectoverall signal strength (or power) of the data be transmitted orreceived. However, by spreading a signal, the amplitude at any one pointtypically will be less than the original (non-spread) signal.

It will be appreciated that increasing the PN code length or decreasingthe chipping rate to achieve a longer communication range will result ina slower data transmission rate. Correspondingly, decreasing the PN codelength or increasing the chipping rate will increase data transmissionrate at a price of reducing communication range.

FIG. 1 schematically illustrates a typical transmitter system 100 of aDSSS system. Original data bits 101 are input to the transmitter system100. The transmitter system includes a modulator 102, a spreadingfunction 104 and a transmit filter 106. The modulator 102 modulates thedata using a well known modulation technique, such as binary phase shiftkeying (“BPSK”), quadrature phase shift keying (QPSK), and complimentarycode keying (CCK). In the case of the BPSK modulation technique, thecarrier is transmitted in-phase with the oscillations of an oscillatoror 180 degrees out-of-phase with the oscillator depending on whether thetransmitted bit is a “0” or a “1”. The spreading function 104 convertsthe modulated original data bits 101 into a PN coded chip sequence, alsoreferred to as spread data. The PN coded chip sequence is transmittedvia an antenna so as to represent a transmitted PN coded sequence asshown at 108.

FIG. 1 also illustrates a typical receiver system or assembly, showngenerally at 150. The receiver system includes a receive filter 152, adespreading function 154, a bandpass filter 156 and a demodulator 158.The PN coded data 108 is received via an antenna and is filtered by thefilter 152. Thereafter, the PN coded data is decoded by a PN codedespreading function 1544. The decoded data is then filtered anddemodulated by the filter 156 and the demodulator 158 respectively toreconstitute the original data bits 101. In order to receive thetransmitted spread data, the receiver system 150 must be tuned to thesame predetermined carrier frequency and be set to demodulate a BPSKsignal using the same predetermined PN code.

More specifically, to receive a spread spectrum transmission signal, thereceiver system must be tuned to the same frequency as the transmitterassembly to receive the data. Furthermore, the receiver assembly mustuse a demodulation technique which corresponds to the particularmodulation techniques used by the transmitter assembly (i.e. same PNcode length, same chipping rate, BPSK). Because multiple mobileterminals may communicate with a common base, each device in thecellular network must use the same carrier frequency and modulationtechnique.

One parameter directly impacted by the practice discussed in thepreceding paragraph is “throughput.” Throughput or the rate of a systemis defined as the amount of data (per second) carried by a system whenit is active. As most communications systems are not able to carry data100% of the time, an additional parameter, throughput is used to measuresystem performance. In general, throughput is defined, as the averageamount of data (per second) carried by the system and is typicallymeasured in bits per second (“bps”). The average is calculated over longperiods of time. Accordingly, the throughput of a system is lower thanits rate. When looking for the amount of data carried, the overheadintroduced by the communication protocol should also be considered. Forexample, in an Ethernet network, the rate is 10 Mbps, but the throughputis only 3 Mbps to 4 Mbps.

One advantage of DSSS systems over FHSS systems is that DSSS systems areable to transmit data 100% of the time, having a high throughput. Forexample, systems operating at 11 Mbps over the air carry about 6.36 Mbpsof data. FHSS systems can not transmit 100% of the available time. Sometime is always spent before and after hopping from one frequency toanother for synchronization purposes. During these periods of time, nodata is transmitted. Obviously, for the same rate over the air, a FHSSsystem will have a lower throughput than an equivalent DSSS system.

Based on the IEEE 802.11 specifications, the maximum number of DSSSsystems that can be collocated is three. These three collocated systemsprovide a brut aggregate throughput of 3×11 Mbps=33 Mbps, or a netaggregate throughput of 3×6.36 Mbps=19.08 Mbps. Because of the rigidallocation of sub-bands to systems, collisions between signals generatedby collocated systems do not occur, and therefore the aggregatethroughput is a linear function of the number of systems. FHSStechnology allows the collocation of much more than 3 systems. However,as the band is allocated in a dynamic way among the collocated systems(they use different hopping sequences which are not synchronized),collisions do occur, lowering the actual throughput. The greater thenumber of collocated systems (base stations or access points), thegreater the number of collisions and the lower the actual throughput.For small quantities of base stations or access points, each additionalbase station or access point brings in almost all its net throughput;the amount of collisions added to the system is not significant. Whenthe number of base stations or access points reaches 15, the amount ofcollisions generated by additional access points is so high that intotal they lower the aggregate throughput. In view of the foregoing,there are some important advantages in using DSSS. It should beappreciated that the terms “access point,” “base station” and“controller” are used interchangeably herein. Furthermore it should beunderstood that in a typical WLAN configuration, an access point (e.g.,transceiver device) connects to a wired network from a fixed locationusing a standard Ethernet cable. Typically, the access point receives,buffers, and transmits data between the wireless network (e.g., WLAN)and a wired network. A single access point can support a small group ofusers and can function within a range of less than one hundred feet toseveral hundred feet. End users access the WLAN through wireless LANadapters, which may be implemented as PC cards in notebook computers,ISA or PCI cards in a desktop computer, or fully integrated deviceswithin hand held computers. The WLAN adapters provide an interfacebetween the client network operating system (NOS) and the airwaves (viaan antenna).

One drawback to using DSSS, relates to the selection of an operatingfrequency when a DSSS access point is added to an existing LAN. In thisregard, when an access point is added to an existing LAN, an operatingfrequency for the access point must be selected. This operatingfrequency is the one which will be used for communications between thenewly added DSSS access point and other communication devices in thenetwork (e.g., mobile units and other access points). In accordance withprior art practice, selection of the operating frequency for the newlyadded DSSS access point is performed manually. More specifically, a userdetermines which frequency is most suitable by determining andevaluating a variety of communication parameters, and then operating acomputer on the network to select an operating frequency for the accesspoint. This manual selection procedure is inefficient and timeconsuming. Moreover, it often does not result in an optimizedconfiguration, and in fact, may result in serious errors in thefrequency selection which impair communications in the existing LAN.With regard to optimized configurations, it should be recognized thatmultiple access points in an LAN may be operating on the same frequency.Therefore, it is desirable to allocate frequencies to access points in amanner which evenly distributes the number of access points operating onthe same frequency. Moreover, in accordance with IEEE 802.11, some ofthe operating frequencies are “overlapping,” while others are“non-overlapping.” It is preferred that “non-overlapping” frequencies beselected, and the number of access points operating on the samefrequencies are evenly distributed. It is also desirable for optimizedcommunications, to evaluate the loads associated with each access point,and its corresponding frequencies. Thus, the operating frequency for thenew access point can be selected such that it is not a frequency used byan access point with a high load.

SUMMARY OF THE INVENTION

In accordance with an example embodiment, there is provided a method forselecting an operating frequency for a communication device The methodcomprises selecting a first frequency, sending a probe signal on thefirst frequency requesting any base unit receiving the probe signal senda response to the probe signal and waiting for a response to the probesignal on the first frequency. The method further comprises selecting asecond frequency, sending a probe signal on the second frequencyrequesting any base unit receiving the probe signal on the secondfrequency send a response to the probe signal and waiting for a responseto the probe signal on the second frequency. A frequency is selectedfrom one of the group consisting of the first frequency and the secondfrequency responsive to not receiving a response to the probe signal onthe selected frequency. An apparatus for implementing the aforementionedmethod is disclosed in an example embodiment.

An advantage of the present invention is the provision of a system forselecting a an operating frequency for a communications device thatautomatically selects an operating frequency by evaluating one or morecommunication parameters of an existing wireless network.

Another advantage of the present invention is the provision of anautomated system for automatically selecting an operating frequency fora communications device based upon a determination of the operatingfrequencies of other communication devices in a wireless network.

Still another advantage of the present invention is the provision of anautomated system for selecting an operating frequency for acommunications device based upon an evaluation of the load of othercommunication devices in a wireless network.

Still another advantage of the present invention is the provision of anautomated system for selecting an operating frequency for acommunications device that selects the operating frequency in such amanner that the operating frequencies of a plurality of communicationdevices in a wireless network is evenly distributed.

Yet another advantage of the present invention is the provision of anautomated system for selecting an operating frequency for acommunications device that selects an optimal non-overlapping operatingfrequency.

Yet another advantage of the present invention is the provision of anautomated system for selecting an operating frequency for acommunication device, wherein the selected operating frequency providesoptimal throughput.

Still other advantages of the invention will become apparent to thoseskilled in the art upon a reading and understanding of the followingdetailed description, accompanying drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangementsof parts, a preferred embodiment and method of which will be describedin detail in this specification and illustrated in the accompanyingdrawings which form a part hereof, and wherein:

FIG. 1 is a schematic representation of a typical transmitter system anda typical receiver system of a DSSS communication system;

FIG. 2A is a schematic representation of a typical wireless LANconfiguration;

FIG. 2B is block diagram of an exemplary embodiment of a typical basestation;

FIG. 3 is a table of DSSS operating frequencies according to the IEEE802.11 standard; and

FIG. 4 is a flow chart of the steps for selecting an operating frequencyfor a communication device, according to a preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

It should be appreciated that a preferred embodiment of the presentinvention as described herein makes particular reference to the IEEE802.11 standard, and utilizes terminology referenced therein. However,it should be understood that reference to the IEEE 802.11 standard andits respective terminology is not intended to limit the scope of thepresent invention. In this regard, the present invention is suitablyapplicable to a wide variety of other communication systems whichutilize a plurality operating frequencies for data transmission.Moreover, it should be appreciated that while the present invention hasbeen described in connection with a wireless local area network (WLAN),the present invention is suitable for use in connection with other typesof wireless networks, including a wireless wide area network (WWAN), awireless metropolitan area network (WMAN) and a wireless personal areanetwork (WPAN).

Referring now to FIG. 2A, there is shown a typical wireless network usedwith the present invention. More specifically, FIG. 2A shows a wirelessLAN system 2 generally comprised of a plurality of communication devicesincluding mobile stations (i.e., portable units 16, 20, 22, 24 and 26,and hand-held unit 18) and a plurality of base stations (or accesspoints or controller) B0, B1, B2, B3 and B4. The base stations may beconnected to a hardwired network backbone or serve as wireless basestations. Each base station can transmit and receive data in itsrespective cell. Wireless LAN system 2 also includes a cable medium,namely, an Ethernet cable 10, along which all network data packets aretransmitted when conveyed between any two network nodes. The principalnodes are direct-wired to the cable 10. These include a work station 12and a network server 14, but may include a mainframe computer,communication channels, shared printers and various mass storage.

In wireless LAN system 2, base station B4 effectively operates as arepeater, coupled to the cable 10 by the base station B3 and a radiolink with the base station B3. Base station B4 has been termed a “basestation” because it registers mobile stations in the same manner as thebase stations that are direct-wired to the cable 10, and offers the samebasic registration services to the mobile stations. The base station B4and each device to which it offers packet transferring services will,however, be registered with the base station B3 to ensure that packetsintended for or transmitted by devices associated with the base stationB4 are properly directed through the base station B4.

Each of the base stations B0-B4 may use DSSS (discussed above) as acommunications protocol. Accordingly, each of the base stations willhave an operating frequency which it utilizes for communications withthe associated mobile units. This operating frequency is selected fromthe list of operating frequencies shown in the table of FIG. 3. In somecases, more than one base unit will be using the same operatingfrequency. When an additional base station, such as base station B5 isadded to a preexisting wireless LAN, the present invention provides asystem for dynamically determining the operating frequency for the newlyadded base station, as will be described in further detail below.

General operation of representative wireless LAN network 2, as discussedabove, is known to those skilled in the art, and is more fully discussedin U.S. Pat. No. 5,276,680, which is fully incorporated herein byreference.

FIG. 2B shows an exemplary embodiment of a typical base unit B. Baseunit B includes conventional components, including an antenna 351 forreceiving and transmitting data via RF, an RF down conversion circuit353, an optional signal level detector 370 (e.g., a conventionalreceived signal strength indicator (RSSI)), a decoder 356, BPSK and QPSKdemodulators 362 a, 362 b which are selectable by switching means 361, amicrocontroller 350, timing control circuit 355, memory 370, userinterface 372, and power supply 374. For transmitting data, Base unit Bfurther includes BPSK and QPSK modulators 366 a, 366 b which areselectable by switch means 365, PN encoder 320, an RF up conversioncircuit 368 and adjustable gain RF output amplifier 369. Thesecomponents are more fully described in U.S. Pat. No. 5,950,124, which isfully incorporated herein by reference. It should be appreciated thatBPSK and QPSK modulators/demodulators are shown only to illustrated thepresent invention, and that other modulation/demodulation techniques arein common use, including BMOK and CCK.

Due to the ever evolving and constantly changing demands of the modernworkplace, it may become advantageous to add additional hardware toexisting wireless network. In particular, it may be beneficial to addone more base stations to an existing wireless network, therebyproviding a larger geographical area of coverage for the network andaccommodating additional users.

One important consideration that must be addressed when adding a basestation to an existing LAN is the need to determine the operatingfrequency of the newly added base station. The selected operatingfrequency will be used to communicate with mobile units that the basestation must support. The physical layer in a network defines themodulation and signaling characteristics for the transmission of data.As previously stated, one typical RF transmission techniques involvesdirect sequence spread spectrum (DSSS). In the United States, DSSS isdefined for operation in the 2.4 GHz (ISM) frequency band, and occupies83 MHz of bandwidth ranging from 2.400 GHz to 2.483 GHz. However, inother geographic regions different frequencies are allocated. FIG. 3shows the frequency allocation in North America, Europe and Japan, inaccordance with IEEE 802.11. As can be readily appreciated from FIG. 3,there are a total of twelve (12) channels capable of supporting the DSSSarchitecture. However, in North America only channels 1-11 areallocated, in Europe only channels 3-11 are allocated and in Japan onlychannel 12 is allocated.

Operation of the present invention will now be described with referenceto FIG. 4. For the purposes of illustrating a preferred embodiment ofthe present invention, it is assumed that base station B5, a directsequence spread spectrum controller, is being added to system 2. Inorder to determine the proper operating frequency for newly added basestation B5, base station B5 must perform a variety of tasks. Basestation B5 interrogates the existing base stations in the wirelessnetwork by broadcasting one or more request signals to the existing basestations in system 2 which request that they return a response signal tobase station B5. All of the existing base stations receiving the requestsignal and operating at the same frequency as the request signal wasbroadcast, will transmit a response signal. Therefore, one or moreresponse signals may be received for each request signal broadcast.

The operating frequencies of the existing base stations is determined bythe fact that a response signal has been returned in response tobroadcast of a request signal at a known frequency. The request signalmay be referred to as a “probe request packet” (e.g., “find router” or“router id packet”), while the response signal may be referred to as a“probe response packet” or “router id.” It should be appreciated thatthe request and response signals may be transmitted between base unitsvia a wireless medium (e.g., RF), or via a wired medium, such as thesystem backbone (e.g., cable 10).

After a request signal is sent at a first frequency, the newly addedbase unit waits a predetermined period of time (e.g., 10 msec) forreceipt of a response signal. If no response signal is received withinthe predetermined time period, then it is assumed that there are noother base units operating on that first frequency. If a response signalis received, then it is determined that there is an existing base unitoperating at that frequency, and optionally the signal strength of theresponse signal is evaluated. A low signal strength (weak signal)indicates a possibly suitable operating frequency selection for thenewly added base unit, whereas a high signal strength (strong signal)indicates a poor selection for the operating frequency of the newlyadded base unit, since interference is likely. Signal strength may bemeasured by a variety of parameters depending on the signal typesrequired for a specific application. Preferably, a conventional receivedsignal strength indicator (RSSI) is used to measure the received signalstrength of an inbound transmission, utilizing well-known techniques. Itshould be appreciated that the same request signal (i.e., samefrequency) may be transmitted multiple times (e.g., 3 times) to providea more accurate determination of operating frequencies. After receivingthe response signal, the base unit will preferably send an acknowledgesignal to the existing base unit that sent the response signal. Thiswill prevent the same base unit from sending additional response signalsto the newly added base unit.

Next, the newly added base unit sends another request signal at adifferent frequency, and conducts the same analysis as above, until allof the appropriate operating frequencies (e.g., see FIG. 3) have beenchecked to determine whether any other base units are using thatfrequency. The newly added base unit will select a suitable operatingfrequency based upon the communication parameter data obtained, namely:(1) a determination of the operating frequencies in use by the otherbase units, (2) a determination of how many base units are using each ofthe operating frequencies, and optionally, and (3) a determination ofsignal strength for each base unit. The selected operating frequencywill preferably not cause interference with communications conducted byexisting base units, and will provide a balanced use of operatingfrequencies such that use of possible operating frequencies among baseunits in the network is evenly distributed.

In a preferred embodiment of the present invention, the newly added basestation will select as an operating frequency the least used,non-overlapping frequency. In this regard, some of the possibleoperating frequencies shown in FIG. 3 are overlapping, while some arenon-overlapping (namely, channels 1, 6 and 11). In this regard, each ofthe listed frequencies is actually the center frequency of the indicatedchannel. Each channel is 22 MHz wide. Thus, channel 1 (center frequency2412 MHz) has frequencies in the range of 2401 MHz to 2423 MHz.Likewise, channel 6 (center frequency 2437 MHz) has frequencies in therange of 2426 MHz to 2448 MHz, while channel 11 (center frequency 2462MHz) has frequencies in the range of 2451 MHz to 2473 MHz. The remainingchannels have frequencies which overlap with at least one frequency ofthe foregoing channels. When non-overlapping frequencies are used, thebase units will not interfere with each other. If two base units operateon the same frequency, then the average throughput, for all associateddevices will drop. Therefore, one objective of the present invention tohave each base unit automatically set their operating frequencies sothat they will not interfere with each other. In selecting among thenon-overlapping frequencies, the newly added base station may alsoconsider balancing the number of base stations operating among thepossible (non-overlapping) frequencies.

In a further embodiment of the present invention, the newly added basestation will also obtain information concerning the load on the otherbase stations, and use this information in selecting its operatingfrequency (in addition to the other information, discussed above). Forinstance, load information may be provided in a data field of theresponse signal in the form of a load value in the range of 1-10,wherein a load value of 10 is indicative of a high load (i.e., largenumber of communications; high traffic) and a load value of 1 isindicative of a low load (i.e., little or no communications; lowtraffic). Additional logic is added to each base unit so that it candetermine its respective load value. The process for selected theoperating frequency of the newly added base station will disfavoroperating frequencies that are in use by existing base units having ahigh load.

It should be appreciated that the present invention contemplates theevaluation of other communication parameters as a means for selectingthe operating frequency of a newly added base unit.

Turning now to FIG. 3, the selection of operating frequencies will bedescribed as each base station is added to system 2. Assuming that basestation B0 is the first base station to be used, a first non-overlappingfrequency is selected (in this case channel 1 at 2.412 GHz). When basestation B1 is added, the furthest distant non-overlapping frequency isselected (i.e., channel 11 at 2.462 GHz). When base station B2 is added,the remaining non-overlapping frequency is selected (channel 6 at 2.437GHz). When base stations B3 and B4 are added to the system, channel 1 isselected base stations B3 and B4 are out of range of base station B0.Again, when base station B5 is added, channel 11 is selected since it isout of range of base station B1.

In general, the first criteria considered when selecting a frequency isto determine whether any non-overlapping are currently available (i.e.,not currently being used). If any non-overlapping frequencies areunused, then an unused non-overlapping frequency is selected. If all ofthe non-overlapping frequencies are in use, then the signal strength isevaluated to determine which base units are in closest range. Thefrequency of the base unit which has the weakest signal strength isfavored for selection of the operating frequency of the newly added baseunit. Next, the load associated with each existing base unit may beconsidered. The frequency in use by a base unit having a high load wouldbe disfavored. It should be appreciated that one or more of theforegoing communication parameters may be considered in selecting theoperating frequency of the newly added base station.

The invention has been described with reference to a preferredembodiment. Obviously, modifications and alterations will occur toothers upon a reading and understanding of this specification. It isintended that all such modifications and alterations be included insofaras they come within the scope of the appended claims or the equivalentsthereof.

1. A method for a wireless base unit to select an operating frequency,comprising: selecting a first frequency; sending a probe signal on thefirst frequency requesting any base unit receiving the probe signal senda response to the probe signal; waiting for a response to the probesignal on the first frequency; selecting a second frequency; sending aprobe signal on the second frequency requesting any base unit receivingthe probe signal on the second frequency send a response to the probesignal; waiting for a response to the probe signal on the secondfrequency; and selecting a selected frequency from one of the groupconsisting of the first frequency and the second frequency responsive todetermining a response was not received to the probe signal on theselected frequency.
 2. The method of claim 1, selecting a selectedfrequency further comprises selecting the least used non-overlappingfrequency.
 3. The method of claim 2, the waiting step further comprisingwaiting a predetermined time period for the response to the requestsignal on the first frequency.
 4. The method of claim 3, wherein thepredetermined time is at least 10 milliseconds.
 5. The method of claim 1wherein the probe signal is one of a probe request packet, a find routerpacket and a router identification packet.
 6. The method of claim 1further comprising sending the probe signal on the first frequency atleast three times and sending the probe signal on the second signal atleast three times.
 7. The method of claim 1, further comprising:receiving a response to the probe signal on the first frequency;measuring the signal strength of the response to the probe signal on thefirst frequency; receiving a response to the probe signal on the secondfrequency; and measuring the signal strength of the response to theprobe signal on the second frequency; wherein the selecting a selectedfrequency selects the frequency measuring the lowest signal strength ofthe response to the probe signal.
 8. The method of claim 1, furthercomprising: receiving at least one response to the probe signal on thefirst frequency; receiving at least one response to the probe signal onthe second frequency; determining how many responses are received on thefirst frequency; determining how many responses are received on thesecond frequency; wherein the selecting the selected frequency selectsthe frequency determined to have the lowest number of responses.
 9. Themethod of claim 1, further comprising: acquiring load data for otherbase stations operating on the first frequency; acquiring load data forother base stations operating on the second frequency; wherein theselecting the selected frequency selects the frequency a lowest load.10. An apparatus, comprising: a base station configured to send andreceive wireless packets on a selected frequency; wherein the basestation is configured to send a probe signal requesting any base stationreceiving the probe signal send a response on a first frequency, and isfurther configured to wait a predetermined amount of time for a responseto the probe signal on the first frequency; wherein the base station isconfigured to send a probe signal requesting any base station receivingthe probe signal send a response on a second frequency, and is furtherconfigured to wait a predetermined amount of time for a response to theprobe signal on the second frequency; and wherein the base stationselects the selected frequency from a group consisting of the firstfrequency and the second frequency upon determining a response to aprobe signal was not received on the selected frequency.
 11. Theapparatus of claim 10, wherein the base station is configured to selectthe operating frequency by selecting the least used non-overlappingfrequency from the group consisting of the first frequency and thesecond frequency responsive to receiving a response to the probe signalon the first signal and a response to the probe signal on the secondfrequency.
 12. The apparatus of claim 10, further comprising: the basestation is configured to receive a response to the probe signal on thefirst frequency and to receive a response to the probe signal on thesecond frequency; the base station is configured to measure the signalstrength of the response received on the first frequency; the basestation is configured to measure the signal strength of the responsereceived on the second frequency; and the base station is furtherconfigured to determine a lowest measured signal strength from the groupconsisting the response received on the first frequency and the responsereceived on the second frequency; wherein the selected frequency is thefrequency with the lowest measured signal strength responsive toreceiving a response to the probe signal on the first signal and aresponse to the probe signal on the second frequency.
 13. The apparatusof 10, further comprising: the base station is configured to receive aresponse to the probe signal on the first signal and to receive aresponse to the probe signal on the second frequency; wherein theresponse to the probe signal on the first frequency comprises a datafield indicative of a load; wherein the response to the probe signal onthe second frequency comprises a data field indicative of a load;wherein the base station is configured to determine a lowest load fromthe response received on the first frequency and the response receivedon the second frequency; wherein the base station is configured toselect the selected frequency based on the frequency having the lowestload responsive to receiving a response to the probe signal on the firstsignal and a response to the probe signal on the second frequency. 14.The apparatus of claim 10, further comprising: the base station isconfigured to receive at least one response to the probe signal on thefirst signal and to receive at least one response to the probe signal onthe second frequency; the base station is configured to determine anumber of responses received on the first frequency; the base station isconfigured to determine a number of responses received on the secondfrequency; and the base station is configured to determine which of thegroup consisting of the first frequency and the second frequencyreceived the lowest number of responses; wherein the selected frequencyis the frequency with the lowest number of responses responsive toreceiving a response to the probe signal on the first signal and aresponse to the probe signal on the second frequency.
 15. The apparatusof claim 10, further comprising: the base station is configured toreceive at least one response to the probe signal on the first frequencyand to receive at least one response to the probe signal on the secondfrequency; the base station is configured to measure the received signalstrengths of responses received on the first frequency and to measurethe received signal strengths of responses received on the secondfrequency; the base station is configured to receive at least oneresponse to the probe signal on the first signal and to receive at leastone response to the probe signal on the second frequency; the basestation is configured to determine a number of responses received on thefirst frequency; and the base station is configured to determine anumber of responses received on the second frequency; wherein the basestation is configured to select the operating frequency by selecting theleast used non-overlapping frequency from the group consisting of thefirst frequency and the second frequency responsive to receiving aresponse to the probe signal on the first signal and a response to theprobe signal on the second frequency.
 16. An apparatus according toclaim 15, further comprising: wherein the at least one response to theprobe signal on the first frequency comprises a data field indicative ofa load; wherein the at least one response to the probe signal on thesecond frequency comprises a data field indicative of a load; whereinthe base station is configured to determine a lowest load from theresponse received on the first frequency and the response received onthe second frequency; wherein determining the least used non-overlappingfrequency is also based on load.
 17. An apparatus according to claim 10,further comprising the base station is configured to send the probesignal a plurality of times the first channel and a plurality of timesof times on the second frequency; and the base station is configured tosend an acknowledgement to base station's responding to the probesignals sent on the first and second frequencies so the responding basestation's only respond once to the plurality of probe signals.
 18. Anapparatus, comprising: means for sending and receiving wireless packetson a selected frequency; means for sending a probe signal requesting anybase station receiving the probe signal send a response on a firstfrequency; means for waiting for a response to the probe signal on thefirst frequency a predetermined amount of time; means for sending aprobe signal requesting any base station receiving the probe signal senda response on a second frequency; means for waiting for a response tothe probe signal on the second frequency a predetermined amount of time;and means for selecting an operating frequency from a group consistingof the first frequency and the second frequency responsive to one of thegroup consisting of the means for waiting for a response to the probesignal on the first frequency and means for waiting for a response tothe probe signal on the second frequency not receiving a response. 19.The apparatus of claim 18, further comprising means for selecting theoperating frequency configured to select the least used non-overlappingfrequency from the group consisting of the first frequency and thesecond frequency responsive to both the means for waiting for a responseto the probe signal on the first frequency and the means for waiting fora response to the probe signal on the second frequency receiving aresponse.